Occupant sensing systems are frequently used in connection with air bags and other pyrotechnically deployed restraints as a means of determining if the restraints should be deployed in the event of sufficiently severe crash. For example, air bag deployment is generally allowed in the case of a normally seated adult occupant, but suppressed in the case of a child or infant seat (both of which are referred to herein as a child seat) placed on the vehicle seat and cinched down with a seat belt or child seat anchor.
One common and generally cost-effective approach to occupant sensing involves installing a fluid-filled bladder under the bottom foam cushion of the vehicle seat and measuring the fluid pressure in the bladder with a pressure-responsive sensor. The under-cushion location of the sensor is preferred because occupant comfort is not affected and because the cushion protects the sensor from sharp objects brought into contact with the exposed surface of the seat. Exemplary systems of this type are disclosed, for example, in the U.S. Pat. Nos. 5,987,370 and 6,246,936 to Murphy et al., and the U.S. Pat. Nos. 6,101,436 and 6,490,936 to Fortune et al., all of which are assigned to Delphi Technologies, Inc., and incorporated herein by reference.
While the above-described sensing approach works well for normally seated occupants, it is still difficult to reliably distinguish between a light-weight normally seated adult (a 5th percentile female adult, for example) and a cinched down child seat because the cinching increases the apparent weight of the child seat. Although it is possible to reliably distinguish between these two types of occupants by sensing the distribution of the occupant weight across the seat, it is difficult to obtain an accurate representation of the actual weight distribution because the occupant weight tends to disperse as it is transmitted through the foam seat cushion to the sensor. Accordingly, what is needed is a cost-effective occupant sensing apparatus having the capability of reliably distinguishing between a cinched child and a normally seated adult of similar apparent weight.